Hydrogen generator and fuel cell system using the same

ABSTRACT

The hydrogen generator includes: a reformer  101  having a reforming catalyst configured to cause a source material and water to react with each other to generate a hydrogen-rich reformed gas; a reformer heater  104  configured to heat the reformer; a carbon monoxide reducing portion  111,121  having a carbon monoxide reducing catalyst configured to reduce carbon monoxide contained in the reformed gas; a carbon monoxide reduction heater  112,123  configured to heat at least one of the carbon monoxide reducing portion, the carbon monoxide reducing catalyst and the reformed gas passing through the carbon monoxide reducing portion; and a controller  200  capable of control such that the carbon monoxide reduction heater is caused to operate in a stop operation period.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydrogen generator configured togenerate hydrogen to be supplied to fuel cells, as well as a fuel cellsystem using the hydrogen generator. More specifically, the inventionrelates to a hydrogen generator configured to heat a carbon monoxidereducing portion during a stop operation period so as to inhibit steamfrom condensing within the carbon monoxide reducing portion, as well asa fuel cell system using the hydrogen generator.

2. Description of the Related Art

Attention is being focused on the fuel cell cogeneration system whichoffers high power generating efficiency and high overall efficiency as adistributed electric power generator capable of effective energyutilization.

Many of fuel cells, including for example the phosphoric acid fuel cellhaving been put to practice and the polymer electrolyte fuel cell(hereinafter will be abbreviated as “PEFC”) under development, generateelectric power using hydrogen as fuel. However, the infrastructure forhydrogen supply has not been established yet and, hence, it is requiredthat hydrogen be generated at the site where a fuel cell system isinstalled.

Seam reforming is a kind of hydrogen generation methods. The steamreforming method is adapted to generate hydrogen by a process including:mixing water vapor with a hydrocarbon material such as natural gas, LPG,gasoline, naphtha, or kerosene, or an alcohol material such as methanol;and allowing a steam reforming reaction of the resulting mixture tooccur in a reformer provided with a reforming catalyst.

The steam reforming reaction produces carbon monoxide (hereinafter willbe referred to as CO) as a by-product and the resulting reformed gascontains about 10% to about 15% of CO. Because CO contained in thereformed gas poisons an electrocatalyst of a PEFC thereby to lower thepower generating performance of the PEFC, a CO reducing portion need beprovided to lower the CO concentration of the reformed gas to 100 ppm orless, preferably 10 ppm or less at the exit of the hydrogen generator.

Usually, the CO reducing portion of the hydrogen generator reduces theCO concentration of the reformed gas to 10 ppm or less by a shifter anda CO removing portion coupled to each other, the shifter having a shiftreaction catalyst configured to cause a water gas shift reaction toproceed in which CO and steam react with each other to produce hydrogenand carbon dioxide, the CO removing portion having at least one of aselective oxidization catalyst configured to cause a selectiveoxidization reaction between oxygen contained in supplied air and CO, ora methanation catalyst configured to methanize CO for CO reduction.

Meanwhile, the PEFC is required to start and stop according to electricpower requirement for its energy utilization efficiency to be improved.The hydrogen generator is also required to start and stop accordingly.

In view of the safety of operation and the durability of the reformingcatalyst, a method has been proposed of purging combustible gasesremaining within the hydrogen generator using the steam in the stopoperation period of the hydrogen generator (see Japanese PatentLaid-Open Publication No. 2002-93447 for example.)

Since the temperatures of respective portions of the hydrogen generatorare relatively high when stopping the hydrogen generator to stop thePEFC in operation, condensation of steam into liquid will not occurwithin the hydrogen generator if purging with steam is followed bypurging and discharging of steam out of the hydrogen generator with airor material gas.

When starting the hydrogen generator, on the other hand, thetemperatures of respective of the shifter and the CO removing portionare raised by a process including: supplying the reformer with a sourcematerial and water from a material supply portion and a water supplyportion, respectively; heating the reformer with a reformer heater toallow the steam reforming reaction to proceed; and passing reformed gasresulting from the steam reforming reaction through the shifter and theCO removing portion thereby to transfer heat from the reformed gas tothe shifter and the CO removing portion.

For this reason, it takes a relatively long time for the temperatures ofthe shifter and CO removing portion to rise sufficiently. In one exampleit took 30 to 40 minutes for the temperatures of the shifter and COremoving portion to rise to higher than 100° C. according to actualtemperature measurement, though depending on the size and structure ofthe hydrogen generator and like factors.

Thus, for example, in cases where the hydrogen generator has to bestopped during the start operation period of the hydrogen generator,particularly the CO reducing portion, which is located on the downstreamside in the hydrogen generator, is often at a temperature close to aroom temperature. If purging with steam is conducted at that time, steamcondenses to liquid water within the CO reducing portion and, in somecases, such condensation occurs on the CO reducing catalyst placedwithin the CO reducing portion undesirably. Such condensation of steamto water on the CO reducing catalyst causes the characteristics of theCO reducing catalyst to deteriorate problematically.

There exists a hydrogen generator using heating means such as a heater.However, the heating means is used to heat the catalyst only in thestart operation period, not in the stop operation period. Therefore, incases where the operation of the hydrogen generator is stoppedimmediately after having been started, the temperature of the COreducing portion is not sufficiently raised and, hence, it is possiblethat the water contained in the purge gas condenses and deteriorates thecatalyst.

In view of the problems essential to the prior art described above, thepresent invention intends to provide a hydrogen generator which isconfigured to inhibit condensation of water within the CO reducingportion during the stop operation period, as well as a fuel cell systemusing the same.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda hydrogen generator comprising: a reformer having a reforming catalystconfigured to cause a source material and water to react with each otherto generate a hydrogen-rich reformed gas; a reformer heater configuredto heat the reformer; a carbon monoxide reducing portion having a carbonmonoxide reducing catalyst configured to reduce carbon monoxidecontained in the reformed gas; a carbon monoxide reduction heaterconfigured to heat at least one of the carbon monoxide reducing portion,the carbon monoxide reducing catalyst and the reformed gas passingthrough the carbon monoxide reducing portion; and a controllerconfigured to perform control such that the carbon monoxide reductionheater is caused to operate in a stop operation period in a manner thata temperature of the carbon monoxide reducing portion is kept higherthan a first predetermined temperature which fails to allow steampresent within the carbon monoxide reducing portion to condense.

In an embodiment of the hydrogen generator according to the first aspectof the present invention, the carbon monoxide reducing portion maycomprise at least one of a shifter and a carbon monoxide removingportion; the carbon monoxide reduction heater may comprise at least oneof a shifter heater and a carbon monoxide removing portion heater; theshifter may have a carbon monoxide reducing catalyst comprising a shiftreaction catalyst; and the carbon monoxide removing portion may have acarbon monoxide reducing catalyst comprising at least one of a selectiveoxidization catalyst and a methanation catalyst.

Another embodiment of the hydrogen generator according to the firstaspect of the present invention may further comprise a carbon monoxidereducing portion temperature sensor configured to detect a temperatureof the carbon monoxide reducing portion, wherein the controller isconfigured to perform control such that the carbon monoxide reductionheater is caused to operate in the stop operation period for at least atime period during which the temperature of the carbon monoxide reducingportion is not higher than the first predetermined temperature.

In another embodiment of the hydrogen generator according to the firstaspect of the present invention, the controller may be configured toperform control such that the carbon monoxide reduction heater is causedto operate in response to a stop instruction to initiate a stopoperation in the stop operation period.

In this embodiment, the controller may be configured to perform controlsuch that the carbon monoxide reduction heater may be caused to stopoperating after lapse of a predetermined time period from issuance ofthe stop instruction in the stop operation period.

Another embodiment of the hydrogen generator according to the firstaspect of the present invention may further comprise a reformertemperature sensor configured to detect a temperature of the reformer,wherein the controller may be configured to perform a control process inthe stop operation period, the control process including: stoppingsupply of the source material and supply of water; causing the carbonmonoxide reduction heater to operate; supplying the source material topurge an interior of said hydrogen generator when the temperaturedetected by the reformer temperature sensor becomes a temperature whichfails to allow carbon to be deposited on the reforming catalyst; andstopping the supply of the source material and the operation of saidcarbon monoxide reduction heater.

Another embodiment of the hydrogen generator according to the firstaspect of the present invention may further comprise a first purge gassupply portion configured to supply a first purge gas; a second purgegas supply portion configured to supply a second purge gas; and areformer temperature sensor configured to detect a temperature of thereformer, wherein the controller may be configured to perform control inthe stop operation period such that: when the temperature detected bythe reformer temperature sensor is lower than a second predeterminedtemperature, the second purge gas supply portion is caused to operateuntil the hydrogen generator becomes fully filled with the second purgegas; and when the temperature detected by the reformer temperaturesensor is not lower than the second predetermined temperature, the firstpurge gas supply portion is caused to operate until the temperaturedetected by said reformer temperature sensor becomes lower than thesecond predetermined temperature and then the second purge gas supplyportion is caused to operate until the hydrogen generator becomes fullyfilled with the second purge gas.

In this embodiment, it is possible that: the first purge gas is steam;the second purge gas is air; and the second predetermined temperature isa temperature which fails to allow the reforming catalyst to beoxidized.

Alternatively, it is possible that: the first purge gas is steam; thesecond purge gas is the source material; and the second predeterminedtemperature is a temperature which fails to allow carbon to be depositedon the reforming catalyst.

Yet alternatively, it is possible that: the first purge gas is one of acombustion exhaust gas and an inert gas.

According to a second aspect of the present invention, there is provideda fuel cell system comprising: a hydrogen generator as recited above;and a fuel cell configured to generate electric power using hydrogengenerated by the hydrogen generator.

The foregoing and other objects, features and attendant advantages ofthe present invention will become more apparent from the reading of thefollowing detailed description of the invention in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of a hydrogengenerator according to embodiment 1 of the present invention;

FIG. 2 is a flowchart illustrating an example of a control programexecuted during the stop operation period of the hydrogen generatorshown in FIG. 1;

FIG. 3 is a block diagram illustrating the configuration of a hydrogengenerator according to embodiment 2 of the present invention;

FIG. 4 is a flowchart illustrating an example of a control programexecuted during the stop operation period of the hydrogen generatorshown in FIG. 3;

FIG. 5 is a block diagram illustrating the configuration of a hydrogengenerator according to embodiment 3 of the present invention;

FIG. 6 is a flowchart illustrating an example of a control programexecuted during the stop operation period of the hydrogen generatorshown in FIG. 5;

FIG. 7 is a flowchart illustrating an example of a control programexecuted during the stop operation period of a hydrogen generatoraccording to embodiment 4 of the present invention;

FIG. 8 is a wiring diagram schematically illustrating the configurationof a controller 200 in embodiment 1 of the present invention; and

FIG. 9 is a block diagram schematically illustrating an example of theconfiguration of a fuel cell system according to embodiment 5 of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will now be describedin detail with reference to the accompanying drawings.

Embodiment 1

Referring first to FIG. 1 illustrating the configuration of a hydrogengenerator 1 according to embodiment 1, the hydrogen generator 1 includesa reformer 101 having a reforming catalyst configured to cause areaction between water and a hydrocarbon material supplied as a sourcematerial to occur to generate a hydrogen-rich gas, a material supplyportion 102 configured to supply the source material to the reformer101, and a water supply portion 103 configured to supply water to thereformer 101.

The reformer 101 is equipped with a reformer heater 104 configured toheat the reformer 101 and a reformer temperature sensor 105 configuredto detect the temperature of the reformer 101. The source material andwater supplied to the reformer 101 are heated thereat by the reformerheater 104, to generate a reformed gas. The heating calories generatedin the reformer heater 104 is determined from the temperature of thereforming catalyst detected by the reformer temperature sensor 105.

The reformer temperature sensor 105 may be configured to detect thetemperature of the reformed gas having passed through the reformingcatalyst. The source material to be supplied from the material supplyportion 102 simply contains a compound comprising at least carbon andhydrogen. Examples of such source materials include hydrocarbonmaterials such as natural gas, LPG, naphtha, gasoline and kerosene, andalcohol materials such as methanol.

Downstream of the reformer 101 in the material feed direction, there isdisposed a shifter 111 having a shift reaction catalyst (not shown)configured to reduce CO contained in the reformed gas fed from thereformer 101 by causing a water gas shift reaction to occur. The shifter111 is equipped with a shifter heater 112 configured to heat the shifter111, a shift reaction catalyst and the reformed gas, and a shiftertemperature sensor 113 configured to detect the temperature of thereformed gas flowing within the shifter 111. Note that: the shifter 111is an embodiment of a carbon monoxide reducing portion defined by thepresent invention; the shift reaction catalyst is an embodiment of acarbon monoxide reducing catalyst defined by the present invention; theshifter heater 112 is an embodiment of a carbon monoxide reductionheater defined by the present invention; and the shifter temperaturesensor 113 is an embodiment of a carbon monoxide reducing portiontemperature sensor defined by the present invention.

In embodiment 1, an electric heater is used as the shifter heater 112and fitted on the exterior of the shifter 111. The shifter heater 112may be any heating device capable of heating the shifter 111 such as aburner or a catalytic combustor without any particular limitation tosuch an electric heater. The shifter temperature sensor 113 may beconfigured to be capable of detecting the temperature of the shiftreaction catalyst.

Downstream of the shifter 111, there is disposed a CO removing portion121 having a CO removing catalyst configured to further reduce COcontained in the reformed gas having passed through the shifter 111. TheCO removing portion 121 is equipped with a CO removing portion heater123 configured to heat at least one of the CO removing portion 121, COremoving catalyst and reformed gas, and a CO removing portiontemperature sensor 124 configured to detect the temperature of thereformed gas flowing within the CO removing portion 121. An air supplyportion 122 is disposed between the CO removing portion 121 and theshifter 111. The CO removing portion 121 is configured to cause aselective oxidization reaction between oxygen contained in air suppliedfrom the air supply portion 122 and CO contained in the reformed gasthereby to reduce the CO concentration of the reformed gas. Note that:the CO removing portion 121 is an embodiment of the carbon monoxidereducing portion defined by the present invention; the CO removingcatalyst is an embodiment of the carbon monoxide reducing catalystdefined by the present invention; the CO removing portion heater 123 isan embodiment of the carbon monoxide reduction heater defined by thepresent invention; and the CO removing portion temperature sensor 124 isan embodiment of the carbon monoxide reducing portion temperature sensordefined by the present invention.

The CO removing catalyst may be a catalyst configured to reduce COcontained in the reformed gas by causing a methanation reaction toproceed. Alternatively, the CO removing catalyst may comprise, incombination, a catalyst causing the selective oxidization reaction toproceed and a catalyst causing the methanation reaction to proceed. Thatis, the CO removing catalyst may comprise either or both of theselective oxidization catalyst configured to catalyze the selectiveoxidization reaction and the methanation catalyst configured to catalyzethe methanation reaction. In embodiment 1, an electric heater is used asthe CO removing portion heater 123 and is fitted on the exterior of theCO removing portion 121. The CO removing portion heater 123 may be anyheating device capable of heating the CO removing portion such as aburner or a catalytic combustor without any particular limitation tosuch an electric heater. The CO removing portion temperature sensor 124may be configured to be capable of detecting the temperature of the COremoving catalyst.

The hydrogen generator 1 according to embodiment 1 includes a purge airsupply portion 106 located upstream of the reformer 101, the purge airsupply portion 106 being configured to supply air during the stopoperation period of the hydrogen generator 1.

In FIG. 1, solid lines represent the feeding-fed relations among thecomponents of the hydrogen generator 1 as to the source material, water,air and hydrogen-rich gas, and solid arrows indicate the directions inwhich the source material, water, air and hydrogen-rich gas are fed.

The hydrogen generator 1 further includes a controller 200 configured tocontrol the heating calories generated in each of the shifter heater 112and the CO removing portion heater 123 and the operation of eachcomponent such as the stop operation of the material supply portion 102,during the stop operation period of the hydrogen generator 1. Thecontroller 200 is communicatively connected to the material supplyportion 102, water supply portion 103, purge air supply portion 106,reformer heater 104, shifter heater 112, CO removing portion heater 123and air supply portion 122 so as to control these components. Further,the controller 200 is communicatively connected to the reformertemperature sensor 105, shifter temperature sensor 113 and CO removingportion temperature sensor 124 so as to receive inputs of signalstherefrom. In FIG. 1, the dotted lines represent the signaltransmitting-receiving connections of the controller 200 with respectiveof other components and the dotted arrows indicate the signaltransmitting directions.

While the carbon monoxide reducing portion according to the presentinvention comprises the shifter 111 and the CO removing portion 121 inembodiment 1, it may comprise only one of the shifter 111 and the COremoving portion 121 selected in accordance with a predeterminedconcentration, if the target CO concentration is equal to or lower thana predetermined concentration.

Description will be made of the controller 200. FIG. 8 is a wiringdiagram schematically illustrating the configuration of the controller200. The controller 200 includes an I/O input port 201, CPU 202, storagedevice 203, I/O output port 204, bus 205, input device 206, and outputdevice 207. The I/O input port 201, CPU 202, storage device 203, I/Ooutput port 204 are interconnected via the bus 205. The input device 206is connected to the I/O input port 201. The output device 207 isconnected to the I/O output port 204. The I/O input port 201 is alsoconnected to the controlled amount detecting devices, i.e., the reformertemperature sensor 105, shifter temperature sensor 113, and CO removingportion temperature sensor 124. The I/O output port 204 is alsoconnected to the controlled components, i.e., the material supplyportion 102, water supply portion 103, reformer heater 104, purge airsupply portion 106, shifter heater 112, air supply portion 122, and COremoving portion heater 123.

In this embodiment, the input device 206 comprises a keyboard or thelike and the output device 207 comprises a display or the like.

The operation of the controller 200 will be described with reference toFIG. 8. The input device 206 inputs set values, including the amount ofhydrogen to be generated, to the CPU 202 via the I/O input port 201. TheCPU 202 stores the information into the storage device 203 as necessary.Signals indicative of controlled amounts detected by the respectivedetecting devices are transferred to the CPU 202 via the I/O input port201. The CPU 202 stores these detected values into the storage device203 as necessary. A control program is pre-stored in the storage device203. The CPU 202 calculates a target controlled value for each of thecontrolled components by using the detected values, control program andthe like stored in the storage device 203. Further, the CPU 202 rewritesthe target controlled values and the like stored in the storage device203 as the need arises from the results of calculation. When necessary,the CPU 202 transmits a signal indicative of an amount of operation oneach controlled component to the controlled component via the I/O outputport 204. The target controlled values, detected values, control programand the like, which are stored in the storage device 203 are outputtedto the output device 207 via the I/O output port 204 so as to beconfirmed by the operator. By the operation of the controller 200 thusdescribed, the values of controlled amounts are detected and controlledand the hydrogen generator 1 is caused to operate.

Here, the hydrogen generator 1 according to embodiment 1 supplies thehydrogen-containing reformed gas having a reduced CO concentration, to aPEFC (polymer electrolyte fuel cell: not shown) where the reformed gasreacts with an oxygen-containing oxidization gas supplied thereto togenerate electric power.

The following description is directed to an example of the operation ofthe hydrogen generator 1, having the above-described configurationaccording to embodiment 1.

During the operation of the hydrogen generator 1 the material supplyportion 102 and water supply portion 103 supply the source material andwater, respectively, to the reforming catalyst accommodated in thereformer 101. The reformer heater 104 heats the reformer 101 so that thetemperature detected by the reformer temperature sensor 105 becomes 650°C., thereby allowing a steam reforming reaction to proceed. The COconcentration of the reformed gas having passed through the reformer 101is about 10%.

The reformed gas having passed through the reformer 101 is fed to theshifter 111 in order for the CO concentration of the reformed gas to bereduced. The shift reaction catalyst accommodated in the shifter 111causes a water gas shift reaction to proceed, thereby reducing COcontained in the reformed gas. The CO concentration of the reformed gashaving passed through the shifter 111 is about 0.3%.

To further reduce CO contained in the reformed gas, the reformed gashaving passed through the shifter 111 is mixed with air supplied fromthe air supply portion 122 and the resulting gas mixture is fed to theCO removing portion 121. The CO concentration of the reformed gas isreduced to 100 ppm or less by a selective oxidization reaction caused bythe CO removing catalyst accommodated in the CO removing portion 121.The reformed gas, the CO concentration of which has been thus reduced,is supplied to the PEFC for electric power generation.

With reference to the flowchart of FIG. 2, description is made of anexample of a control program executed during the stop operation periodof the hydrogen generator 1 according to embodiment 1. The “stopoperation”, as used herein, is meant to include the operation ofstopping hydrogen generation in all cases including not only the case ofstop running but also the case of suspension. The “stop operationperiod” is meant by a time period from a stop instruction is issueduntil the hydrogen generator 1 stops operating, during which a series ofoperations are performed.

Initially, in step S1, the controller 200 causes the reformer heater 104to stop operating.

Subsequently, in step S2, the controller 200 determines whether or notthe temperature detected by the shifter temperature sensor 113 or by theCO removing portion temperature sensor 124 is not higher than 100° C.,which is an example of a first predetermined temperature defined by thepresent invention.

Here, the first predetermined temperature is the dew point of steamwithin each of the shifter 111 and CO removing portion 121. In the stopoperation period, the internal pressure of each of these components ishigher than atmospheric pressure, and when purging with steam isconducted, the partial pressure of steam within each of those componentsis approximately 100% and the dew point therewithin is approximately100° C. For this reason, the first predetermined temperature is set to100° C. in the following description. In some cases, however, the firstpredetermined temperature is not necessarily 100° C. depending on theinternal pressure or the partial pressure of steam. Therefore, the firstpredetermined temperature may be any temperature which fails to allowsteam to condense within the shifter 111 or CO removing portion 121,that is, any temperature higher than the dew point, without anyparticular limitation to 100° C.

Subsequently, if the temperature detected by the shifter temperaturesensor 113 or by the CO removing portion temperature sensor 124 is nothigher than 100° C., in step S3, the controller 200 causes the shifterheater 112 and the CO removing portion heater 123 to operate to startheating the shifter 111 and CO removing portion 121. At this time, thecontroller 200 controls heating so that the temperature detected by eachof the shifter temperature sensor 113 and the CO removing portiontemperature sensor 124 is kept higher than 100° C. This heating stepinhibits steam supplied thereafter from condensing on the shift reactioncatalyst or the CO removing catalyst and allows steam to be dischargedoutside the hydrogen generator 1.

Subsequently, in step S4, the controller 200 determines whether or notthe temperature detected by the reformer temperature sensor 105 is notlower than 200° C., which is an example of a second predeterminedtemperature defined by the present invention. This determination isconducted because if air is supplied when the temperature of thereformer 101 is not lower than 200° C., the reforming catalyst isoxidized and deteriorated by air.

If the temperature of the reformer 101 is determined to be not lowerthan 200° C. in step S4, the controller 200 stops the operation of thematerial supply portion 102 in step S5. By stopping the operation of thematerial supply portion 102 while keeping the water supply from thewater supply portion 103, supplied water is evaporated into steam, whichis an example of the first purge gas defined by the present invention,within the reformer 101. In this embodiment, the water supply portion103 serves as the first purge gas supply portion defined by the presentinvention. Steam thus produced passes through the shifter 111 and the COremoving portion 121 to purge residual combustible gas mainly comprisinghydrogen from the hydrogen generator 1 and then is discharged outsidethe hydrogen generator 1.

Subsequently, in step S6, the controller 200 causes the reformertemperature sensor 105 to continue temperature detection until thetemperature detected by the reformer temperature sensor 105 becomeslower than 200° C.

Subsequently, in step S7, after the temperature within the reformer 101has decreased to lower than 200° C., the controller 200 stops theoperation of the water supply portion 103, thereby stopping the supplyof steam.

In step S8, in turn, the controller 200 causes the purge air supplyportion 106 to start operating and continue operating for apredetermined time period. By doing so, the supplied air purges residualsteam from the interior of the hydrogen generator 1 and is thendischarged outside the hydrogen generator 1. This means that thisembodiment uses air as the second purge gas defined by the presentinvention. The purge air supply portion 106 in this embodiment serves asthe second purge gas supply portion defined by the present invention.The aforementioned predetermined time period is sufficient to purgesteam from the interior of the hydrogen generator 1. However, if thetemperature of each of the shifter 111 and the CO removing portion 121does not reach 100° C. at the beginning of or before the beginning ofstep S8, purging with air needs to be performed for the predeterminedtime period from the time 100° C. is reached even though the operationof purging with air in step S8 has already started. If purging withsteam is conducted in a state where 100° C. is not reached yet, it ispossible that steam condenses. However, by conducting purging with airfor the predetermined time period from the time 100° C. is reached,condensed water can be evaporated and discharged.

Subsequently, in step S9, after the interior of the hydrogen generator 1has been completely purged with air, the controller 200 stops theoperation of each of the shifter heater 112 and the CO removing portionheater 123.

Finally, in step S10, the controller 200 causes the purge air supplyportion 106 to stop supplying air. In this way, the stop operation ofthe hydrogen generator 1 is completed.

On the other hand, if both of the temperatures detected by respective ofthe shifter temperature sensor 113 and the CO removing portiontemperature sensor 124 are determined to be higher than 100° C. in stepS2, steam condensation does not occur even under a condition in whichheating is not conducted. For this reason, the process proceeds to stepS14 without causing the shifter heater 112 and CO removing portionheater 123 to operate.

In step S14, in turn, the controller 200 determines whether or not thetemperature within the reformer 101 is not lower than 200° C. as in stepS4.

Subsequently, in step S15, the operation of the material supply portion102 is stopped as in step S5.

Subsequently, in step S16, temperature detection is continued until thetemperature detected by the reformer temperature sensor 105 becomeslower than 200° C. as in step S6.

Subsequently, in step S17, after the temperature within the reformer 101has decreased to lower than 200° C., the operation of the water supplyportion 103 is stopped as in step S7.

Subsequently, in step S18, the operation of the purge air supply portion106 is started and continued for the predetermined time period. By doingso, the supplied air purges residual steam from the interior of thehydrogen generator 1 completely, as in step S8.

Finally, in step S10, the supply of air from the purge air supplyportion 106 is stopped.

If the temperature detected by the reformer temperature sensor 105 isdetermined to be lower than 200° C. in step S4 or step S14, thereforming catalyst will not be oxidized due to purging with air (secondpurge gas) even if the interior of the hydrogen generator 1 is notpurged with steam (first purge gas). For this reason, when thetemperature within the reformer 101 is lower than 200° C., the processproceeds from step S4 to step S11 in which the operation of each of thematerial supply portion 102 and the water supply portion 103 is stoppedand then to step S8 in which air supply is conducted. From step S14, theprocess proceeds to step S12 in which the operation of each of thematerial supply portion 102 and the water supply portion 103 is stoppedand then to step S18.

In this way, the temperature within each of the shifter 111 and the COremoving portion 121 can be kept higher than 100° C. by the stopoperation in which the shifter heater 112 and the CO removing portionheater 123 are caused to operate. For this reason, steam used for purgedoes not condense within each of the shifter 111 or the CO removingportion 121. Further, since there is no possibility that steam remainsand condenses within each of the shifter 111 and the CO removing portion121, the catalytic characteristics of the catalysts used therein can beinhibited from deteriorating.

The stop operation described above may be performed not only when thehydrogen generator 1 is in an unsteady operation state like a state justafter start but also when the hydrogen generator 1 is in a steadyoperation state.

While both of the shifter 111 and the CO removing portion 121 are heatedin step S3 if the temperature within the shifter 111 or the CO removingportion 121 is determined to be not higher than 100° C. in steps S2,heating may be conducted for only one of these components, thetemperature of which is not higher than 100° C.

While steps S2, S4 and S14 are each followed by one of different stepswhich is selected depending on the result of determination, steps S1 toS10 except steps S2, S4 and S14 may be conducted regardless of thetemperatures of these components, which means that determinations insteps S2, S4 and S14 may be omitted. Since it is possible that thereforming catalyst is oxidized and deteriorated by the supplied air whenthe internal temperature of the reformer 101 is not lower than 200° C.,it is preferable to conduct determination in step S6.

While the operations of respective of the shifter heater 112 and the COremoving portion heater 123 are stopped in step S9, they may be stoppedin any step without limitation to step S9. For example, the controller200 may perform control such that, with the temperatures withinrespective of the shifter 111 and the CO removing portion 121 beingmonitored by the shifter temperature sensor 113 and the CO removingportion temperature sensor 124, the shifter heater 112 and the COremoving portion heater 123 are caused to operate when the temperaturewithin one of the shifter 111 and the CO removing portion 121 becomesnot higher than 100° C. and stop operating when the temperature becomeshigher than 100° C.

If the temperature within the shifter 111 or the CO removing portion 121is determined to be higher than 100° C. in step S2, steps S14 to S18 areperformed without the shifter heater 112 and CO removing portion heater123 operating, it is possible that with the temperature within each ofthe shifter 111 and the CO removing portion 121 being monitored, theshifter heater 112 and the CO removing portion heater 123 are caused tooperate when the temperature becomes not higher than 100° C.

It is possible that step S2 in which the controller 200 determineswhether or not the temperature of the shifter 111 or the CO removingportion 121 is not higher than 100° C. and step S3 in which the shifterheater 112 and the CO removing portion heater 123 are caused to operateare performed just before step 8 in which the operation of the purge airsupply portion 106 is started. Alternatively, steps S2 and S3 may beperformed with the purge air supply portion 106 operating to purge theinterior of the hydrogen generator 1 with air. In any case, the shifterheater 112 and the CO removing portion heater 123 may be caused tooperate at any time as long as the temperature of each of the shifter111 and the CO removing portion 121 can be adjusted to inhibit condensedwater from remaining within each of the shifter 111 and the CO removingportion 121.

In this embodiment, the shifter temperature sensor 113 and the COremoving portion temperature sensor 124 are configured to monitor thetemperatures within respective of the shifter 111 and within the COremoving portion 121. However, it is possible to determine whether ornot to cause the shifter heater 112 and the CO removing portion heater123 to operate based on physical values related to the temperaturewithin each of the shifter 111 and the CO removing portion 121. Examplesof such physical values include the temperature of the reformer 101detected by the reformer temperature sensor 105, an elapsed time fromthe start of the operation of the hydrogen generator 1, the amount ofwater supplied to the reformer 101, and the humidity within each of theshifter 111 and the CO removing portion 121.

The hydrogen generator 1 according to this embodiment is not necessarilyused in fuel supply to PEFCs and can find use in fuel supply to othertypes of fuel cells and applications in chemical plants or the likerequiring generation of high purity hydrogen.

Embodiment 2

FIG. 3 is a block diagram illustrating the configuration of a hydrogengenerator 1 according to embodiment 2. Embodiment 2 is different fromembodiment 1 in that: neither the shifter 111 nor the CO removingportion 121 is equipped with a temperature sensor; and the shifterheater 112 and the CO removing portion heater 123 are caused to operateregardless of the temperature of each of the shifter 111 and the COremoving portion 121. That is, the shifter 111 and the CO removingportion 121 are heated regardless the temperature of the componentsduring the stop operation period without determination based on thetemperatures thereof. Like reference characters are used to designatelike or corresponding parts throughout FIGS. 1 and 3 and the descriptionof such parts will be omitted.

With reference to FIG. 4, description will be made of an example of acontrol program executed during the stop operation period of thehydrogen generator 1 according to embodiment 2. The “stop operation”, asused herein, is meant to include the operation of stopping hydrogengeneration in all cases including not only the case of stop running butalso the case of suspension. The “stop operation period” is meant by atime period from a stop instruction is issued until the hydrogengenerator stops operating during which a series of operations areperformed. The stop operation process of embodiment 2 is different fromthat of embodiment 1 in that determination step 2 (of determiningwhether or not the temperature of the shifter 111 or the CO removingportion 121 is not higher than 100° C.) and the steps branched therefromare omitted.

Initially, in step S21, the controller 200 causes the reformer heater104 to stop operating.

Subsequently, in step S22, the controller 200 causes the shifter heater112 and the CO removing portion heater 123 to operate to start heatingthe shifter 111 and CO removing portion 121. This heating step inhibitssteam supplied thereafter from condensing on the shift reaction catalystand the CO removing catalyst and allows steam to be discharged outsidethe hydrogen generator 1. The capacity of each of the shifter heater 112and CO removing portion heater 123 and the heating time and intensityare appropriately established so as to inhibit steam condensation withineach of the shifter 111 and CO removing portion 121 and obviate damageto the shifter 111 and CO removing portion 121 due to possible excessivetemperature elevation.

Subsequently, in step S23, the controller 200 determines whether or notthe temperature detected by the reformer temperature sensor 105 is notlower than 200° C., which is an example of the second predeterminedtemperature defined by the present invention. This determination isconducted because if air is supplied when the temperature of thereformer 101 is not lower than 200° C., the reforming catalyst isoxidized and deteriorated by air.

If the temperature of the reformer 101 is determined to be not lowerthan 200° C. in step S23, the controller 200 stops the operation of thematerial supply portion 102 in step S24. By stopping the operation ofthe material supply portion 102 while keeping the water supply from thewater supply portion 103, the supplied water is evaporated into steam,which is an example of the first purge gas defined by the presentinvention, within the reformer 101. Steam thus produced passes throughthe shifter 111 and the CO removing portion 121 and is dischargedoutside the hydrogen generator 1 while purging residual combustible gasmainly comprising hydrogen from the hydrogen generator 1. In thisembodiment, the water supply portion 103 serves as a first purge gassupply portion defined by the present invention.

Subsequently, in step S25, the controller 200 causes the reformertemperature sensor 105 to continue temperature detection until thetemperature detected by the reformer temperature sensor 105 becomeslower than 200° C.

Subsequently, in step S26, after the temperature within the reformer 101has been lowered to lower 200° C., the controller 200 stops theoperation of the water supply portion 103, thereby stopping the supplyof steam.

In step S27, in turn, the controller 200 causes the purge air supplyportion 106 to start operating and continue operating for apredetermined time period. By doing so, the supplied air purges residualsteam from the interior of the hydrogen generator 1 and is dischargedoutside the hydrogen generator 1. This means that this embodiment usesair as the second purge gas defined by the present invention. The purgeair supply portion 106 in this embodiment serves as a second purge gassupply portion defined by the present invention.

Subsequently, in step S28, after the interior of the hydrogen generator1 has been completely purged with air, the controller 200 stops theoperation of each of the shifter heater 112 and the CO removing portionheater 123.

Finally, in step S29, the controller 200 causes the purge air supplyportion 106 to stop supplying air. In this way, the stop operation ofthe hydrogen generator 1 is completed.

On the other hand, if the temperature detected by the reformertemperature sensor 105 is determined to be lower than 200° C. in stepS23, the reforming catalyst will not be oxidized by purging with air(second purge gas) even if the interior of the hydrogen generator 1 isnot purged with steam (first purge gas). For this reason, when thetemperature within the reformer 101 is not higher than 200° C., theprocess proceeds to step S30 in which the operation of each of thematerial supply portion 102 and the water supply portion 103 is stoppedand then to step S27 in which air supply is conducted.

In this embodiment 2, the shifter heater 112 and the CO removing portionheater 123 are caused to operate regardless of whether or not thetemperature of the shifter 111 or the CO removing portion 121 is higherthan 100° C. Therefore, unlike embodiment 1, this embodiment does notneed the provisions of the shifter temperature sensor 113 and COremoving portion temperature sensor 124, which can lead to a simplifieddevice construction and reduced cost.

The time at which the shifter heater 112 and the CO removing portionheater 123 are caused to operate or stop may vary depending on thedevice construction, the catalysts used, or the like and hence is notlimited to that described in this embodiment. The shifter heater 112 andthe CO removing portion heater 123 may be caused to operate at any timeas long as the temperature of each of the shifter 111 and the COremoving portion 121 can be adjusted to inhibit condensed water fromremaining within each of the shifter 111 and the CO removing portion121.

The hydrogen generator 1 according to this embodiment is not necessarilyused in fuel supply to PEFCs and can find use in fuel supply to othertypes of fuel cells and applications in chemical plants or the likerequiring generation of high purity hydrogen.

Notes on Embodiments 1 and 2

The predetermined temperatures may be varied depending on the deviceconstruction, catalysts used, or the like and are not limited to thespecific temperatures described in embodiments 1 and 2.

The stop operation processes described in embodiments 1 and 2 areillustrative and, hence, there is no limitation thereto. In embodiment1, for example, it is possible that step S2 (determination of thetemperature within each of the shifter 111 and the CO removing portion121) is performed and then heating is started before step S1 (stop ofthe operation of the reformer heater 104). Also, it is possible thatstep S10 (stop of the operation of the purge air supply portion 106)precedes step S9 (stop of the operations of shifter heater 112 and COremoving portion heater 123). In embodiment 2, similarly, step S22 mayprecede step S21 and step S29 may precede step S28.

The water supply portion 103 configured to supply water for thereforming reaction in each of embodiments 1 and 2 also serves as thefirst purge gas supply portion defined by the present invention. Whilethe first purge gas defined by the present invention is steam in each ofembodiments 1 and 2, it may be feed gas, inert gas, or combustionexhaust gas resulting from the operation of the reformer heater 104,shifter heater 112 or CO removing portion heater 123.

In each of the embodiments 1 and 2, the second purge gas supply portiondefined by the present invention corresponds to the purge air supplyportion 106, and the second purge gas corresponds to air. However, it ispossible that the purge air supply portion 106 is omitted and the sourcematerial may be used as the second purge gas. That is, the sourcematerial may be supplied from the material supply portion 102 in orderto purge and discharge steam.

In each of embodiments 1 and 2, inert gas may be used to purge theinterior of the hydrogen generator 1 in the stop operation period. Evenin this case, steam remaining within the reformer 101 will not condenseto liquid water in each of the shifter 111 and the CO removing portion121.

The program defined by the present invention is a program which isconfigured to cause the controller of the hydrogen generator 1 of thepresent invention to function by means of a computer and hencecooperates with the computer.

The storage medium used in the present invention is a storage mediumwhich contains therein a program configured to cause all or some of thefunctions of the controller of the hydrogen generator 1 of the presentinvention to be performed by means of a computer and which allows theprogram to be read by the computer for the program to cooperate with thecomputer.

The function of the controller defined by the present invention is meantto include all or part of the functions of the controller.

In one form of use of the program, the program is stored on acomputer-readable storage medium and cooperates with a computer.

In another form of use of the program, the program is transmittedthrough a transmission medium, read by a computer and cooperates withthe computer.

Examples of data structures for use in the present invention includedatabase, data format, data table, and different types of data.

Examples of such recording media include ROM and the like. Examples ofsuch transmission media include such a transmission medium as Internet,and light, radio waves, and sonic waves.

The aforementioned computer used in the present invention may includenot only such sheer hardware as a CUP but also firmware, OS, andperipheral devices.

The configuration according to the present invention may be implementedeither as a software configuration or as a hardware configuration.

Embodiment 3

FIG. 5 is a block diagram illustrating the configuration of a hydrogengenerator 1 according to embodiment 3. Embodiment 3 is different fromembodiment 1 in that a combustible gas mainly comprising hydrogen ispurged with steam, which in turn is purged and discharged with thesource material. Therefore, the configuration shown in FIG. 5 does notinclude the purge air supply portion 106 included in embodiment 1. Likereference characters are used to designate like or corresponding partsthroughout FIGS. 1 and 5 and the description of such parts will beomitted.

With reference to the flowchart of FIG. 6, description will be made ofan example of a control program executed during the stop operationperiod of the hydrogen generator 1 according to embodiment 3. The “stopoperation”, as used herein, is meant to include the operation ofstopping hydrogen generation in all cases including not only the case ofstop running but also the case of suspension. The “stop operationperiod” is meant by a time period from the issuance of a stopinstruction until the hydrogen generator stops operating during which aseries of operations are performed.

Initially, in step S31, the controller 200 causes the reformer heater104 to stop operating.

Subsequently, in step S32, the controller 200 determines whether or notthe temperature detected by the shifter temperature sensor 113 or by theCO removing portion temperature sensor 124 is not higher than 100° C.,which is an example of the first predetermined temperature defined bythe present invention.

Subsequently, if the temperature detected by the shifter temperaturesensor 113 or by the CO removing portion temperature sensor 124 is nothigher than 100° C., in step S33, the controller 200 causes the shifterheater 112 and the CO removing portion heater 123 to operate to startheating the shifter 111 and CO removing portion 121. At this time, thecontroller 200 controls heating so that the temperature detected by eachof the shifter temperature sensor 113 and the CO removing portiontemperature sensor 124 is kept higher than 100° C. This heating stepinhibits steam supplied thereafter from condensing on the shift reactioncatalyst and the CO removing catalyst and allows steam to be dischargedoutside the hydrogen generator 1.

Subsequently, in step S34, the controller 200 determines whether or notthe temperature detected by the reformer temperature sensor 105 is notlower than 400° C., which is an example of the second predeterminedtemperature defined by the present invention. This determination isconducted because if only the source material is supplied with thesupply of water stopped when the temperature of the reformer 101 is notlower than 400° C., carbon is deposited on the reforming catalyst anddeteriorates the catalytic characteristics thereof.

If the temperature of the reformer 101 is determined to be not lowerthan 400° C. in step S34, the controller 200 stops the operation of thematerial supply portion 102 in step S35. By stopping the operation ofthe material supply portion 102 while keeping the water supply from thewater supply portion 103, the supplied water is evaporated into steam,which is an example of the first purge gas defined by the presentinvention, within the reformer 101. Steam thus produced passes throughthe shifter 111 and the CO removing portion 121 to purge residualcombustible gas mainly comprising hydrogen from the hydrogen generator 1and is discharged outside the hydrogen generator 1. In this embodiment,the water supply portion 103 serves as the first purge gas supplyportion defined by the present invention.

Subsequently, in step S36, the controller 200 causes the reformertemperature sensor 105 to continue temperature detection until thetemperature detected by the reformer temperature sensor 105 becomeslower than 400° C.

Subsequently, in step S37, after the temperature within the reformer 101has decreased to lower than 400° C., the controller 200 stops theoperation of the water supply portion 103, thereby stopping the supplyof steam.

In step S38, in turn, the controller 200 causes the material supplyportion 102 to resume operating and continue operating for apredetermined time period. By doing so, the supplied source materialpurges residual steam from the interior of the hydrogen generator 1 andis discharged outside the hydrogen generator 1. This means that thisembodiment uses the source material as the second purge gas defined bythe present invention. And, the material supply portion 102 in thisembodiment serves as the second purge gas supply portion defined by thepresent invention. The aforementioned predetermined time period is atime period sufficient to purge steam from the interior of the hydrogengenerator 1. However, if the temperature of each of the shifter 111 andthe CO removing portion 121 does not reach 100° C. at the beginning ofor before the beginning of step S38, purging with the source materialneeds to be performed for the predetermined time period from the time100° C. is reached even though the purging with the source material instep S38 has already started. If purging with steam is conducted in astate where 100° C. is not reached yet, it is possible that steamcondenses. However, by conducting purging with the source material forthe predetermined time period from the time 100° C. is reached,condensed water can be evaporated and discharged.

Subsequently, in step S39, after the interior of the hydrogen generator1 has been completely purged with the source material, the controller200 stops the operation of each of the shifter heater 112 and the COremoving portion heater 123.

Finally, in step S40, the controller 200 causes the material supplyportion 102 to stop supplying the source material. In this way, the stopoperation of the hydrogen generator 1 is completed.

On the other hand, if both of the temperatures detected by respective ofthe shifter temperature sensor 113 and the CO removing portiontemperature sensor 124 are determined to be higher than 100° C. in stepS32, steam condensation does not occur even under a condition in whichheating is not conducted. For this reason, the process proceeds to stepS44 without causing the shifter heater 112 and CO removing portionheater 123 to operate.

In step S44, in turn, the controller 200 determines whether or not thetemperature within the reformer 101 is not lower than 400° C. as in stepS34.

Subsequently, in step S45, the operation of the material supply portion102 is stopped as in step S35.

Subsequently, in step S46, temperature detection is continued until thetemperature detected by the reformer temperature sensor 105 becomeslower than 400° C. as in step S36.

Subsequently, in step S47, after the temperature within the reformer 101has decreased to lower than 400° C., the operation of the water supplyportion 103 is stopped as in step S37.

Subsequently, in step S48, the operation of the material supply portion102 is resumed and continued for the predetermined time period. By doingso, the interior of the hydrogen generator 1 is completely purged withthe source material supplied, as in step S38.

Finally, in step S40, the supply of the source material from thematerial supply portion 102 is stopped.

If the temperature detected by the reformer temperature sensor 105 isdetermined to be lower than 400° C. in step S34 or step S44, carbon willnot be deposited on the reforming catalyst and will not therebydeteriorate the catalytic characteristics thereof due to purging withthe source material even if the interior of the hydrogen generator 1 isnot purged with steam. For this reason, when the temperature within thereformer 101 is lower than 400° C., the process proceeds from step S34to step S49 in which the operation of the water supply portion 103 isstopped and then to step S39. From step S44 the process proceeds to stepS50 in which the operation of the water supply portion 103 is stoppedand then to step S40.

In this way, the temperature within each of the shifter 111 and the COremoving portion 121 can be kept higher than 100° C. by the stopoperation in which the shifter heater 112 and the CO removing portionheater 123 are caused to operate. For this reason, steam used for purgedoes not condense within each of the shifter 111 and the CO removingportion 121. Further, since there is no possibility that steam remainsand condenses within each of the shifter 111 and the CO removing portion121, the catalytic characteristics of the catalysts used therein can beinhibited from deteriorating.

The stop operation described above may be performed not only when thehydrogen generator 1 is in an unsteady operation state like a state justafter the start but also when the hydrogen generator 1 is in a steadyoperation state.

While both of the shifter 111 and the CO removing portion 121 are heatedin step S33 if the temperature within the shifter 111 or the CO removingportion 121 is determined to be not higher than 100° C. in step S32,heating may be conducted for only one of these components, thetemperature of which is lower than 100° C.

While steps S32, S34 and S44 are each followed by one of different stepswhich is selected depending on the result of determination, steps S31 toS40 except steps S32, S34 and S44 may be conducted regardless of thetemperatures of the components, which means that determinations in stepsS32, S34 and S44 may be omitted. If only the supply of the sourcematerial is performed with the supply of water stopped when the internaltemperature of the reformer 101 is not lower than 400° C., it ispossible that deposition of carbon on the reforming catalyst occurs anddeteriorates the catalytic characteristics of the reforming catalyst.Therefore, it is preferable to conduct determination of step S36.

While the operations of respective of the shifter heater 112 and the COremoving portion heater 123 are stopped in step S39, they may be stoppedin any step without limitation to step S39. For example, control may beperformed such that, with the temperatures within respective of theshifter 111 and the CO removing portion 121 being monitored by theshifter temperature sensor 113 and the CO removing portion temperaturesensor 124, the shifter heater 112 and the CO removing portion heater123 are caused to operate when the temperature within one of the shifter111 and the CO removing portion 121 becomes not higher than 100° C. andstop operating when the temperature becomes higher than 100° C.

In the above described embodiments, when the temperature within theshifter 111 or the CO removing portion 121 is determined to be higherthan 100° C. in step S32, steps S44 to S48 are performed without theshifter heater 112 and CO removing portion heater 123 operating.Alternatively, the shifter heater 112 and the CO removing portion heater123 may be caused to operate when the temperature becomes not higherthan 100° C. with the temperature within each of the shifter 111 and theCO removing portion 121 being monitored.

It is possible that step S32 in which the controller 200 determineswhether or not the temperature of the shifter 111 or the CO removingportion 121 is not higher than 100° C. and step S33 in which the shifterheater 112 and the CO removing portion heater 123 are caused to operateare performed just before step S38 in which the operation of thematerial supply portion 102 is resumed. Alternatively, steps S32 and S33may be performed with the material supply portion 102 operating to purgethe interior of the hydrogen generator 1 with the source material. Inany case, the shifter heater 112 and the CO removing portion heater 123may be caused to operate at any time as long as the temperature of eachof the shifter 111 and the CO removing portion 121 can be adjusted toinhibit condensed water from remaining within each of the shifter 111and the CO removing portion 121.

As in embodiment 2, the shifter 111 and the CO removing portion 121 maybe heated regardless of the temperatures of the components during thestop operation without determination based on the temperatures thereof.In this case, the shifter 111 and the CO removing portion 121 need notbe equipped with respective temperature sensors.

The hydrogen generator 1 according to this embodiment is not necessarilyused in fuel supply to PEFCs and can find use in fuel supply to othertypes of fuel cells and applications in chemical plants or the likerequiring generation of high purity hydrogen.

Embodiment 4

The configuration of a hydrogen generator 1 according to embodiment 4 isalso illustrated in the block diagram of FIG. 5 used in embodiment 3.This embodiment 4 is different from embodiment 3 in that purging withthe source material is performed without the purging with steam.

With reference to the flowchart of FIG. 7, description will be made ofan example of a control program executed during the stop operationperiod of the hydrogen generator 1 according to embodiment 4. The “stopoperation”, as used herein, is meant to include the operation ofstopping hydrogen generation in all cases including not only the case ofstop running but also the case of suspension. The “stop operationperiod” is meant by a time period from when a stop instruction is issueduntil the hydrogen generator stops operating during which a series ofoperations are performed.

Initially, in step S51, the controller 200 causes the reformer heater104 to stop operating.

Subsequently, in step S52, the controller 200 determines whether or notthe temperature detected by the shifter temperature sensor 113 or by theCO removing portion temperature sensor 124 is not higher than 100° C.,which is an example of the first predetermined temperature defined bythe present invention.

Subsequently, if the temperature detected by the shifter temperaturesensor 113 or by the CO removing portion temperature sensor 124 is nothigher than 100° C., in step S53, the controller 200 causes the shifterheater 112 and the CO removing portion heater 123 to operate to startheating the shifter 111 and CO removing portion 121. At this time thecontroller 200 controls heating so that the temperature detected by eachof the shifter temperature sensor 113 and the CO removing portiontemperature sensor 124 is kept higher than 100° C. This heating stepinhibits steam to be supplied later from condensing on the shiftreaction catalyst and the CO removing catalyst and allows steam to bedischarged outside the hydrogen generator 1.

Subsequently, in step S54, the controller 200 determines whether or notthe temperature detected by the reformer temperature sensor 105 is notlower than 400° C., which is an example of the second predeterminedtemperature defined by the present invention. This determination isconducted because if only the source material is simply supplied withoutthe water supply under the condition in which the temperature of thereformer 101 is not lower than 400° C., carbon may be deposited on thereforming catalyst and deteriorate the catalytic characteristicsthereof.

If the temperature of the reformer 101 is determined to be not lowerthan 400° C. in step S54, the controller 200 stops the operation of eachof the material supply portion 102 and the water supply portion in stepS55.

Subsequently, in step S56, the controller 200 causes the reformertemperature sensor 105 to continue temperature detection until thetemperature detected by the reformer temperature sensor 105 becomeslower than 400° C.

Subsequently, after the temperature within the reformer 101 hasdecreased to lower than 400° C., in step S57, the controller 200 causesthe material supply portion 102 to resume operating and continueoperating for a predetermined time period. By doing so, the sourcematerial supplied is discharged outside the hydrogen generator 1 whilepurging residual combustible gas mainly comprising hydrogen from theinterior of the hydrogen generator 1. The aforementioned predeterminedtime period is a time period sufficient to purge steam from the interiorof the hydrogen generator 1. However, if the temperature of each of theshifter 111 and the CO removing portion 121 does not reach 100° C. atthe beginning of or before the begging of step S57, purging with thesource material needs to be performed for the predetermined time periodfrom the time 100° C. is reached even though the operation of purgingwith the source material in step S57 has already started. If purgingwith steam is conducted in a state where 100° C. is not reached yet, itis possible that steam condenses. However, by conducting purging withthe source material for the predetermined time period from the time 100°C. is reached, condensed water can be evaporated and discharged.

Subsequently, in step S58, after the interior of the hydrogen generator1 has been completely purged with the source material, the controller200 stops the operation of each of the shifter heater 112 and the COremoving portion heater 123.

Finally, in step S59, the controller 200 causes the material supplyportion 102 to stop supplying the source material. In this way, the stopoperation of the hydrogen generator 1 is completed.

On the other hand, if both of the temperatures detected by respective ofthe shifter temperature sensor 113 and the CO removing portiontemperature sensor 124 are determined to be higher than 100° C. in stepS52, steam condensation does not occur even under a condition in whichheating is not conducted. For this reason, the process proceeds to stepS64 without causing the shifter heater 112 and the CO removing portionheater 123 to operate.

In step S64, in turn, the controller 200 determines whether or not thetemperature within the reformer 101 is not lower than 400° C. as in stepS54.

Subsequently, in step S65, the operation of each of the material supplyportion 102 and the water supply portion 103 is stopped as in step S55.

Subsequently, in step S66, temperature detection is continued until thetemperature detected by the reformer temperature sensor 105 becomeslower than 400° C. as in step S56.

Subsequently, after the temperature within the reformer 101 hasdecreased to lower than 400° C., in step S67, the operation of thematerial supply portion 102 is resumed and continued for thepredetermined time period. By doing so, the interior of the hydrogengenerator 1 is completely purged with the source material supplied as instep S57.

Finally, in step S59, the supply of the source material from thematerial supply portion 102 is stopped.

If the temperature detected by the reformer temperature sensor 105 isdetermined to be lower than 400° C. in step S54 or step S64, carbon willnot be deposited on the reforming catalyst and will not deteriorate thecatalytic characteristics thereof due to purging with the sourcematerial even if the interior of the hydrogen generator 1 is not purgedwith steam. For this reason, when the temperature within the reformer101 is not higher than 400° C., the process proceeds from step S54 tostep S68 in which the operation of the water supply portion 103 isstopped and then to step S58. Alternatively, the process proceeds fromstep S64 to step S69 in which the operation of the water supply portion103 is stopped and then to step S59.

In this way, the temperature within each of the shifter 111 and the COremoving portion 123 can be kept higher than 100° C. by the stopoperation in which the shifter heater 112 and the CO removing portionheater 123 are caused to operate. For this reason, steam used for purgedoes not condense within each of the shifter 111 and the CO removingportion 121. Since there is no possibility that steam remains andcondenses within each of the shifter 111 and the CO removing portion121, the catalytic characteristics of the catalysts used therein can beinhibited from deteriorating. Further, since the omission of theoperation of purging with water shortens the duration of exposure of thecatalysts to steam, the catalytic characteristics of the catalysts canbe further inhibited from deteriorating.

The stop operation described above may be performed not only when thehydrogen generator 1 is in an unsteady operation state like a state justafter the start but also when the hydrogen generator 1 is in a steadyoperation state.

When the temperature within the shifter 111 or the CO removing portion121 is determined to be not higher than 100° C. in step S52 and S53,both of the shifter 111 and the CO removing portion 121 are heated,heating may be conducted for only one of these components, thetemperature of which is lower than 100° C.

While steps S52, S54 and S64 are each followed by one of different stepswhich is selected depending on the result of determination, steps S51 toS59 except steps S52, S54 and S64 may be conducted regardless of thetemperatures of the components, which means that determinations in stepsS52, S54 and S64 may be omitted. Since it is possible that deposition ofcarbon on the reforming catalyst occurs and thereby deteriorates thecatalytic characteristics of the reforming catalyst if the supply ofonly the source material is performed with the supply of water stoppedwhen the internal temperature of the reformer 101 is not lower than 400°C., it is preferable to conduct determination of step S56.

While the operations of respective of the shifter heater 112 and the COremoving portion heater 123 are stopped in step S58, they may be stoppedat any time without limitation to step S58. For example, control may beperformed such that with the temperatures within respective of theshifter 111 and the CO removing portion 121 being monitored by theshifter temperature sensor 113 and the CO removing portion temperaturesensor 124, the shifter heater 112 and the CO removing portion heater123 are caused to operate when the temperature within one of the shifter111 and the CO removing portion 121 becomes not higher than 100° C. andstop operating when the temperature becomes higher than 100° C.

While, if the temperature within the shifter 111 or the CO removingportion 121 is determined to be higher than 100° C. in step S52, stepsS64 to S67 are performed without the shifter heater 112 and CO removingportion heater 123 operating, it is possible that with the temperaturewithin each of the shifter 111 and the CO removing portion 121 beingmonitored, the shifter heater 112 and the CO removing portion heater 123are caused to operate when the temperature becomes not higher than 100°C.

It is possible that step S52 in which the controller 200 determineswhether or not the temperature of each of the shifter 111 or the COremoving portion 121 is not higher than 100° C. and step S53 in whichthe shifter heater 112 and the CO removing portion heater 123 are causedto operate are performed just before step S57 in which the operation ofthe material supply portion 102 is resumed. Alternatively, steps S52 andS53 may be performed with the material supply portion 102 operating topurge the interior of the hydrogen generator 1 with the source material.In any case, the shifter heater 112 and the CO removing portion heater123 may be caused to operate at any time as long as the temperature ofeach of the shifter 111 and the CO removing portion 121 can be adjustedso to inhibit condensed water from remaining within each of the shifter111 and the CO removing portion 121.

As in embodiment 2, the controller 200 may be configured to cause theshifter heater 112 and the CO removing portion heater 123 to operate fora predetermined time period. In this case, the shifter 111 and the COremoving portion 121 need not be equipped with respective temperaturesensors.

The hydrogen generator 1 according to this embodiment is not necessarilybe used in fuel supply to PEFCs and can find use in fuel supply to othertypes of fuel cells and applications in chemical plants or the likerequiring generation of high purity hydrogen.

Embodiment 5

This embodiment is a fuel cell system 2 including the hydrogen generator1 according to any one of embodiments 1 to 4, and a fuel cell. The fuelcell system 2 uses the hydrogen-rich gas generated by the hydrogengenerator 1 as a fuel for the fuel cell 125.

FIG. 9 is a block diagram schematically illustrating an example of theconfiguration of the fuel cell system 2 according to this embodiment.The fuel cell system 2 shown in FIG. 9 includes the fuel cell 125 inaddition to the hydrogen generator 1 of embodiment 1. For this reason,like reference characters are used to designate like or correspondingparts throughout FIGS. 1 and 9 and description of such parts will beomitted.

The fuel cell 125 generates electric power by using a hydrogen-rich gasas a fuel. The fuel cell 125 has a fuel supply port connected to the COremoving portion 121. The hydrogen-rich gas generated by the hydrogengenerator 1 is supplied to the fuel cell 125. This embodiment uses, forexample, a polymer electrolyte fuel cell (PEFC) as the fuel cell 125.

The fuel cell system 2 having such a configuration is capable ofinhibiting water condensation within the carbon monoxide reducingportion during the stop operation period. Accordingly, the catalystsused in the carbon monoxide reducing portion can be inhibited fromdeteriorating, which leads to a prolonged lifetime of the fuel cellsystem.

It is to be noted that this embodiment may use a hydrogen generator 1according to any one of embodiments 2 to 4 instead of the hydrogengenerator 1 according to embodiment 1.

While only certain presently preferred embodiments of the presentinvention have been described in detail, as will be apparent for thoseskilled in the art, certain changes and modifications may be made inembodiments without departing from the spirit and scope of the presentinvention as defined by the following claims.

1. A hydrogen generator comprising: a reformer having a reformingcatalyst configured to cause a source material and water to react witheach other to generate a hydrogen-rich reformed gas; a reformer heaterconfigured to heat said reformer; a carbon monoxide reducing portionhaving a carbon monoxide reducing catalyst configured to reduce carbonmonoxide contained in the reformed gas; a carbon monoxide reductionheater configured to heat at least one of said carbon monoxide reducingportion, the carbon monoxide reducing catalyst and the reformed gaspassing through said carbon monoxide reducing portion; and a controllerconfigured to perform control such that said carbon monoxide reductionheater is caused to operate in a stop operation period in a manner thata temperature of said carbon monoxide reducing portion is kept higherthan a first predetermined temperature which fails to allow steampresent within said carbon monoxide reducing portion to condense.
 2. Thehydrogen generator according to claim 1, wherein said carbon monoxidereducing portion comprises at least one of a shifter and a carbonmonoxide removing portion, said carbon monoxide reduction heatercomprises at least one of a shifter heater and a carbon monoxideremoving portion heater, said shifter has a carbon monoxide reducingcatalyst comprising a shift reaction catalyst, and said carbon monoxideremoving portion has a carbon monoxide reducing catalyst comprising atleast one of a selective oxidization catalyst and a methanationcatalyst.
 3. The hydrogen generator according to claim 1, furthercomprising: a carbon monoxide reducing portion temperature sensorconfigured to detect a temperature of said carbon monoxide reducingportion, wherein said controller is configured to perform control suchthat said carbon monoxide reduction heater is caused to operate in thestop operation period for at least a time period during which thetemperature of said carbon monoxide reducing portion is not higher thanthe first predetermined temperature.
 4. The hydrogen generator accordingto claim 1, wherein said controller is configured to perform controlsuch that said carbon monoxide reduction heater is caused to operate inresponse to a stop instruction to initiate a stop operation in the stopoperation period.
 5. The hydrogen generator according to claim 4,wherein said controller is configured to perform control such that saidcarbon monoxide reduction heater is caused to stop operating after lapseof a predetermined time period from issuance of the stop instruction inthe stop operation period.
 6. The hydrogen generator according to claim1, further comprising: a reformer temperature sensor configured todetect a temperature of said reformer, wherein said controller isconfigured to perform a control process in the stop operation period,the control process including: stopping supply of the source materialand supply of water; causing said carbon monoxide reduction heater tooperate; supplying the source material to purge an interior of thehydrogen generator when the temperature detected by said reformertemperature sensor becomes a temperature which fails to allow carbon tobe deposited on the reforming catalyst; and stopping the supply of thesource material and the operation of said carbon monoxide reductionheater.
 7. The hydrogen generator according to claim 1, furthercomprising: a first purge gas supply portion configured to supply afirst purge gas; a second purge gas supply portion configured to supplya second purge gas; and a reformer temperature sensor configured todetect a temperature of said reformer, wherein said controller isconfigured to perform control in the stop operation period such that:when the temperature detected by said reformer temperature sensor islower than a second predetermined temperature, said second purge gassupply portion is caused to operate until said hydrogen generatorbecomes fully filled with the second purge gas, and when the temperaturedetected by said reformer temperature sensor is not lower than thesecond predetermined temperature, said first purge gas supply portion iscaused to operate until the temperature detected by said reformertemperature sensor becomes lower than the second predeterminedtemperature and then said second purge gas supply portion is caused tooperate until said hydrogen generator becomes fully filled with thesecond purge gas.
 8. The hydrogen generator according to claim 7,wherein the first purge gas is steam, the second purge gas is air, andthe second predetermined temperature is a temperature which fails toallow the reforming catalyst to be oxidized.
 9. The hydrogen generatoraccording to claim 7, wherein the first purge gas is steam, the secondpurge gas is the source material, and the second predeterminedtemperature is a temperature which fails to allow carbon to be depositedon the reforming catalyst.
 10. The hydrogen generator according to claim7, wherein the first purge gas is one of a combustion exhaust gas and aninert gas.
 11. A fuel cell system comprising: a hydrogen generatorincluding: a reformer having a reforming catalyst configured to cause asource material and water to react with each other to generate ahydrogen-rich reformed gas; a reformer heater configured to heat saidreformer; a carbon monoxide reducing portion having a carbon monoxidereducing catalyst configured to reduce carbon monoxide contained in thereformed gas; a carbon monoxide reduction heater configured to heat atleast one of said carbon monoxide reducing portion, the carbon monoxidereducing catalyst and the reformed gas passing through said carbonmonoxide reducing portion; and a controller configured to performcontrol such that said carbon monoxide reduction heater is caused tooperate in a stop operation period in a manner that a temperature ofsaid carbon monoxide reducing portion is kept higher than a firstpredetermined temperature which fails to allow steam present within saidcarbon monoxide reducing portion to condense; and a fuel cell configuredto generate electric power using hydrogen generated by said hydrogengenerator.